Your truck should do fine.
Air down right after you get on the sand and DONT let off the gas. Air down to between, 10-15 psi in the tires. Depending on how soft the sand is, drop your pressure lower.
Observe which direction the wind is blowing so you know which side of the dunes the drop offs will be. Generally the wind is comming from the ocean, so the drop offs will be facing away from the ocean.
Make sure you have someplace on your truck someone can hook a tow strap to so they can pull you out. (tow hooks or a hitch) And make sure you have a tow strap.
DONT do anything you dont feel comfortable doing, that will just get you in trouble.
I would recommend NOT going into the dunes a few hours before and after noon, it is extremely difficult to see the dunes when there arent any shadows.
Thats all I can think of right now...O, and DONT go over 5mph next to the water, or you just might get a ticket.
EDIT: ONE more VERY important thing: MAKE SURE YOU HAVE A FLAG AT ALL TIMES!!!! This insures people will see you while you are out in the dunes and its illegal not to have one.
EDIT AGAIN: I thought of more.
NEVER stop going up a dune...you will just get stuck.
Always stop facing down hill.
Make sure you are always with other people, it sucks getting stuck out there by yourself.
Drive around on sand highway for awhile before you go out into the larger stuff.
Keep your lights on so that people will be able to see you easier while you are out in the dunes.
Dont go down the face of a dune too fast, the bottom of the dune will most likely be at a smaller angel then you think...and this could happen to your truck...
Dont stop on the side of a dune, just keep going. If you do stop, and dont feel comfortable continuing, have someone who has experience out there drive your truck out.
You can pull the ABS fuse while you are out there...this will help you stop on the dunes and prevent the ABS from kicking in...which is really annoying.